A geologist studying a remote volcanic island discovers goats with unusual survival adaptations. The geologist barely survives the goats, which attack him in a degrading way. When events years later draw him and his new bride back to the island, they discover the attack produced an offspring and must decide the fate of the fantastic semi-human "child." Is it a bizarre, but explicable, biological accident or something evil? Ancient texts from Irish monks who once inhabited the isle suggest the "child's" true father may not be the geologist but one who dwells beneath the island's volcanic plume.